# sim-codec-mcp
In one line: It reads and writes the message envelopes of the Model Context Protocol, checking each one is well formed.
## What it gives you
The Model Context Protocol is a standard way for tools and models to exchange messages -- requests, notifications, replies, and errors, each wrapped in a JSON-RPC envelope. This reads one such envelope at a time and turns it into a checked value, and writes a value back out as a proper envelope. Its whole job is that envelope: confirming it is complete and correctly shaped, and translating faithfully between the wire message and the runtime's own form. It deliberately leaves the bigger questions -- how a message is routed, how it travels, what it triggers -- to other parts of the system. That narrow focus means you can trust that any envelope passing through has been validated, with mistakes caught at the door.
## Why you will be glad
- Every message envelope is checked for correct shape before anything relies on it.
- Standard-protocol messages translate cleanly into the runtime's own values.
- Malformed or out-of-scope input is refused rather than passed along.
## Where it fits
This is a focused, domain member of the SIM codec family. It handles just the message envelopes of the Model Context Protocol, giving the runtime a validated entry and exit point for that standard while leaving routing and delivery to their own libraries.